A fairly common complication for patients with cavus foot type who begin wearing orthosis is to develop pain on the dorsum of the foot secondary to shoe pressure.
Without orthotic devices, the foot is allowed to collapse somewhat and this will decrease pressure on the dorsum of the foot. This collapse does, of course, often lead to the symptoms that brought the patient into your practice in the first place and clinicians often treat these symptoms with foot orthoses. However, by placing an orthosis under the arch of the foot, particularly one that conforms well to the arch, it can have the effect of increasing pressure on the dorsum of the foot.
There are several options to address this issue.
The first and most important option is to advise all patients with cavus feet of this possibility prior to casting them for orthotic devices. One should advise them that they will likely need to get new shoes that fit with the orthoses. In most cases, the patient can easily find shoes that will fit their foot and the orthosis, and not result in excessive pressure on the top of the foot.
In cases in which the foot is very high arched leading to greater than average instep volume patients may require extra-depth shoes. I often recommend the brand Aetrex which offers models that look like normal walking or running shoes but provide extra depth.
The second treatment option is to modify the lacing pattern of the shoe so you avoid having laces going across the foot at the painful area.
The third option is to adjust the orthosis in a way to decrease pressure from the shoe on the top of the foot. The most effective way to do this is to first grind the heel of the orthosis as thin as possible so it sits low in the shoe. With a polypropylene orthosis, you can grind this to be essentially paper thin. In addition, you can thin the arch of the orthosis in the mid-arch. Use a grinder to grind from the bottom of the orthosis. By slightly thinning the orthosis, you will increase the flexibility of the device, letting both the foot and the orthosis collapse a bit, thus decreasing pressure on the dorsum of the foot.
Finally, I advised these patients that some of the softer athletic shoes that have been popular recently, such as the Nike Free, tend to be quite shallow and often do not accommodate high arched feet very well, particularly when one adds an orthosis.
Editor's note: This blog was originally published at www.prolaborthotics.com/Blog/tabid/90/EntryID/501/Default.aspx  and has been adapted with permission from Lawrence Huppin, DPM, and ProLab Orthotics. For more information, visit www.prolaborthotics.com  .